Spinal fusion is a procedure that involves joining two or more adjacent vertebrae with a bone fixation device to restrict movement of the vertebra with respect to one another. Spinal fixation devices are used in spine surgery to align, stabilize and/or fix a desired relationship between adjacent vertebral bodies. Such devices typically include a spinal fixation element, such as, for example, a relatively rigid fixation rod, a dynamic or flexible spinal rod, etc. (collectively referred to herein as a longitudinal rod), that is coupled to adjacent vertebrae by attaching the spinal fixation element to various bone fixation elements, such as, for example, hooks, bolts, wires, screws, etc. (collectively referred to herein as a bone anchor). The bone anchor may commonly include heads with channels in which the longitudinal rod is inserted and subsequently clamped by a set screw or closure cap. Surgeons may commonly choose to install multiple bone anchors, as well as multiple longitudinal rods, to treat a given spinal disorder. The longitudinal rods may have a predetermined contour, and once installed, the longitudinal rod may hold the vertebrae in a desired spatial relationship, either until desired healing or spinal fusion has taken place, or for some longer period of time.
Surgeons have often encountered difficulty installing such devices because of trouble aligning the longitudinal rod(s) with the channels in the heads of the bone anchors. For example, the heads of bone anchors may often be out of vertical and/or horizontal alignment with one another because of the curvature of the spine or the size and shape of each vertebra.
The process of positioning and setting known bone anchors may be tedious and relatively time-consuming, typically requiring more than one surgical tool to clamp the longitudinal rods and the bone anchors in desired positions. Even with a high degree of skill and care, the process of positioning an assembly of known bone anchors and longitudinal rods, and clamping said bone anchors and longitudinal rods in place can take more time than desired during a surgical procedure, and may even result in longitudinal rods, bone anchors, or both moving out of position before clamping is completed.
Thus, it is desirable to have a spinal fixation device (also referred to herein as a clamp) that can secure longitudinal rods and bone anchors in place with a minimal amount of time and a minimal number of surgical tools. It is also desirable to have a clamp that can secure a longitudinal rod at an axis that is offset or laterally displaced from the axis of the bone anchor.